File formats demystified

Raster Images Explained

Also called bitmap graphics, these are digital images composed of tiny rectangular pixels, or picture elements, that are arranged in a grid in such a way that an image is formed. It’s also referred to as a bitmap since it has information that is mapped directly to the display’s pixel grid. The word raster was borrowed from the term ‘raster scan,’ which was how old CRT monitors displayed images, by magnetically steering a concentrated electron beam line by line to form an image.

The file size of these images depends directly on the color depth and the number of pixels being used in the image. This means that a typical 8 bit image with a 1280×720 resolution will contain 921,600 pixels ( 112.5K file size) while a full HD 1920×1080 image will have 2,073,600 pixels (253.1K file size).

The main disadvantage to these images are their dependence on resolution. They can be scaled down with no visible changes in quality, but when the resolution is scaled up, quality loss is unavoidable. The image will look either blocky and pixelated, or blurry depending on the method used to scale the image. Vector graphics, on the other hand, are able to be scaled up to any size because they use geometry and mathematical equations to define images rather than directly mapping pixels in a grid. Vector graphics are better suited for typesetting and graphic design.

Since this file format stores much more information, they require larger file sizes and can be a bit difficult to work with when used for large format work. Fortunately, there are already image compression techniques and algorithms that have been created to address that problem with a minimal effect on the image quality. There are many file formats that qualify as Raster but the most common are .jpg, .tiff, .gif, and .bmp.

For information on Vector based images, please click here.

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If you still have questions, please feel free to contact your Welch representative.